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Abstract:

Disclosed are compositions and methods for separating gangue material from
metallic sulfide ores. The compositions typically include a
lignosulfonate and do not include a cyanide salt. Suitable
lignosulfonates may include lignosulfonates, for example hardwood
lignosulfonate having a weight average molecular weight of about 3 kDa to
about 12 kDa and having a relatively low sulfur content and a relatively
low sulfonate content.

Claims:

1. An ore slurry comprising:(a) a metal sulfide ore;(b) water;(c) a
hardwood lignosulfonate, wherein:(i) the lignosulfonate has a weight
average molecular weight of about 3 kDa to about 12 kDa;(ii) the
lignosulfonate has a total sulfur content of less than about 10.0% (w/w);
and(iii) the lignosulfonate has a sulfonate content of less than about
7.5% (w/w); and(d) a processing reagent for facilitating separation of a
metal sulfide present in the ore from gangue.

2. The ore slurry of claim 1, wherein the slurry does not comprise cyanide
or a salt thereof.

3. The ore slurry of claim 1 or 2, wherein the processing reagent is a
reagent selected from the group consisting of a flotation reagent, a
frothing reagent, a collector reagent, and an extractor reagent.

4. The ore slurry of any of claims 1-3, wherein the lignosulfonate has a
λmax of 276-277 nm.

5. The ore slurry of any of claims 1-4, wherein the hardwood
lignosulfonate has a pH of less than about 9.0 in aqueous solution.

6. The ore slurry of any of claims 1-5, wherein the hardwood
lignosulfonate is derived from a Eucalyptus tree, a Maple tree, or a
Birch tree.

7. The ore slurry of any of claims 1-6, wherein the ore comprises copper
sulfide.

8. The ore slurry of any of claims 1-6, wherein the ore comprises zinc
sulfide.

9. The ore slurry of any of claims 1-6, wherein the ore comprises lead
sulfide.

10. The ore slurry of any of claims 1-9, wherein the ore comprises an iron
compound selected from the group consisting of pyrrhotite, pyrite, and
marcasite.

11. The ore slurry of any of claims 1-10, wherein the slurry has a pH that
is greater than about 9.

12. The ore slurry of any of claims 1-11, wherein the slurry has a pH that
is between about 9.5 and about 11.5.

13. The ore slurry of any of claims 1-12, wherein the hardwood
lignosulfonate is present in the ore slurry at a concentration of about
250-500 g/mt.

14. The ore slurry of any of claims 1-13, wherein the salt of the
lignosulfonate is selected from the group consisting of sodium
lignosulfonate, potassium lignosulfonate, calcium lignosulfonate, or
mixtures thereof.

15. The ore slurry of any of claims 1-14, wherein the processing reagent
is an aliphatic alcohol having 3-12 carbons which may be straight-chain,
branched, or cyclic.

17. The ore slurry of any of claims 1-16, wherein the processing reagent
is a xanthate.

18. The ore slurry of any of claims 1-17, wherein the processing reagent
is a reagent selected from the group consisting of a thionocarbamate, a
thiophosphate, and a thiourea.

19. The ore slurry of any of claims 1-18, wherein the processing reagent
is a surfactant.

20. The ore slurry of any of claims 1-19, further comprising sodium
carbonate.

21. The ore slurry of any of claims 1-20, further comprising calcium
hydroxide.

22. The ore slurry of any of claims 1-21, wherein the slurry does not
comprise any of the following components: starch; dextrin or dextrin that
has been treated with an alkaline solution; quebracho; guar gum; or
polyacrylate.

23. A method of recovering the metal sulfide from the ore slurry of any of
claims 1-22, the method comprising:(a) introducing air into the ore
slurry to create a frothed fraction, wherein the metal sulfide is at
least partially suspended in the frothed fraction; and(b) removing the
frothed fraction from the ore slurry, thereby recovering the metal
sulfide.

24. A method of recovering a metal sulfide from an ore, the method
comprising:(a) adding to the ore a hardwood lignosulfonate, wherein:(i)
the lignosulfonate has a weight average molecular weight of about 3 kDa
to about 12 kDa;(ii) the lignosulfonate has a total sulfur content of
less than about 10.0% (w/w); and(iii) the lignosulfonate has a sulfonate
content of less than about 7.5% (w/w); and(b) adding to the ore a
processing reagent for facilitating separation of a metal sulfide present
in the ore from gangue;(c) preparing a slurry of the ore, wherein the ore
slurry has a pH that is basic;(d) introducing air into the ore slurry to
create a frothed fraction, wherein the metal sulfide is at least
partially suspended in the frothed fraction; and(e) removing the frothed
fraction from the ore slurry, thereby recovering the metal sulfide.

25. The method of claim 24, wherein the method does not comprise adding
cyanide or a salt thereof to the ore or the ore slurry.

26. The method of claim 24 or 25, wherein the processing reagent is a
reagent selected from the group consisting of a flotation reagent, a
frothing reagent, a collector reagent, and an extractor reagent.

27. The method of any of claims 24-26, wherein the lignosulfonate has a
λmax of 276-277 nm.

28. The method of any of claims 24-27, wherein the hardwood lignosulfonate
has a pH of less than about 9.0 in aqueous solution.

29. The method of any of claims 24-28, wherein the hardwood lignosulfonate
is derived from a Eucalyptus tree, a Maple tree, or a Birch tree.

30. A method of recovering a metal sulfide from an ore, the method
comprising:(a) preparing an ore slurry, wherein the ore slurry has a pH
that is basic.(b) adding to the ore slurry a hardwood lignosulfonate,
wherein:(i) the lignosulfonate has a weight average molecular weight of
about 3 kDa to about 12 kDa;(ii) the lignosulfonate has a total sulfur
content of less than about 10.0% (w/w); and(iii) the lignosulfonate has a
sulfonate content of less than about 7.5% (w/w);(c) adding to the ore
slurry a processing reagent for facilitating separation of a metal
sulfide present in the ore from gangue;(d) introducing air into the ore
slurry to create a frothed fraction, wherein the metal sulfide is at
least partially suspended in the frothed fraction; and(e) removing the
frothed fraction from the ore slurry, thereby recovering the metal
sulfide.

31. The method of claim 30, wherein the method does not comprise adding
cyanide or a salt thereof to the ore or the ore slurry.

32. The method of claim 30 or 31, wherein the processing reagent is a
reagent selected from the group consisting of a flotation reagent, a
frothing reagent, a collector reagent, and an extractor reagent.

33. The method of any of claims 30-32, wherein the lignosulfonate has a
λmax of 276-277 nm.

34. The method of any of claims 30-33, wherein the hardwood lignosulfonate
has a pH of less than about 9.0 in aqueous solution.

35. The method of any of claims 30-34, wherein the hardwood lignosulfonate
is derived from a Eucalyptus tree, a Maple tree, or a Birch tree.

Description:

BACKGROUND

[0001]The invention relates to compositions which contain and methods
which utilize lignosulfonates for separating gangue materials from
metallic sulfide ores.

[0002]Froth flotation is a physical-chemical method of recovering,
concentrating, or isolating ground ores. The process involves chemical
treatment of an ore pulp or slurry to create conditions favorable for the
attachment of selected mineral particles to air bubbles created by
passing a stream of air through the ore pulp or slurry. The air bubbles
carry the selected minerals to the surface of the pulp and form a
stabilized froth which is skimmed from the surface and contains the
selected mineral particles. Other non-selected minerals remain dispersed
in the pulp or slurry.

[0003]Froth flotation has been used as a method for concentrating valuable
metallic sulfides for about a century. In froth flotation, sulfide
mineral particles in an ore slurry are treated with a processing agent
(or collector) that facilitates their flotation and transport by the air
bubbles to the surface of the slurry, where the frothed fraction forms.
This process has proven to be an economic method of concentrating many
simple sulfide ores, where relatively non-selective oils may be used as
collectors. However, more complex ores having gangue materials, such as
Cu--Fe, Cu--Pb--Zn--Fe, Pb--Zn--Fe, Cu--Zn--Fe, and Cu--Ni--Fe ores
require a process that is more selective. Gangue materials typically are
considered to include iron containing compounds such as the iron-sulfur
compounds pyrrhotite, pyrite, and marcasite. Iron is undesirable because
it has to be removed in the smelting stage. Additionally, iron (e.g., in
the form of pyrite) can effect efficiency of metal extraction in leaching
reactions. Therefore, the less iron an ore contains after a concentration
process, then the less costly final recovery of the desired ore will be.

[0004]The need to treat such complex sulfide ores has resulted in the
development of more selective reagents and reagent combinations.
Xanthates have proven to be useful as selective collectors for sulfide
minerals. Another common method for obtaining a concentration of
desirable metallic sulfides is to depress gangue materials during the
flotation of sulfide ore. Sodium cyanide, sodium hydrosulfide, and sodium
thiophosphates commonly are used as selective flotation depressants in
combination with selective collectors. For example, gangue material
(e.g., pyrite) often are depressed by addition of large amounts of
calcium hydroxide. In this process, the pH of the bulk slurry is
increased and pyrite becomes hydrophilic. Materials rendered hydrophilic
tend to be rejected during the flotation process. However, when lime
addition is not an acceptable solution (for example where the process
must be performed at an intermediate pH, or where iron compounds are not
sufficiently rejected even at high pH) then sodium cyanide (or one of the
above-mentioned reagents) is often used as a depressant for non-desired
minerals, including iron sulfides. However, components like sodium
cyanide are hazardous and toxic. As such, chemicals like sodium cyanide
are highly regulated and require expensive handling equipment in order to
use them in froth flotation.

[0005]This invention relates to the use of lignosulfonates during the
flotation of sulfide ores. In particular, the invention relates to the
use of lignosulfonates derived from hardwood sources. The disclosed
lignosulfonate compositions are shown to be effective gangue depressants
and provide a method for eliminating the use of hazardous or toxic
chemicals, such as cyanides, during the flotation of massive sulfide
ores. In particular, the disclosed lignosulfonate compositions are shown
to act as a direct replacement for cyanide during the flotation of zinc,
lead, and copper ores. These lignosulfonates compositions give equal or
superior performance in comparison to other toxic gangue depressants such
as sodium cyanide.

[0006]U.S. Pat. Nos. 5,693,692; 5,049,612; 4,952,329; 4,880,529; and
4,877,517 disclose gangue depressant compositions that include
lignosulfonate. However, the lignosulfonate used in the gangue depressant
compositions of these patents, i.e., Kelig 100, differs from the
lignosulfonates used in the present application not only functionally but
also structurally. First, Kelig 100 is processed in a different way than
the lignosulfonates disclosed herein, which substantially increases the
polymer's sulfonate and sulfur content and renders the polymer much more
hydrophilic than the polymers used in the present disclosure. In
addition, Kelig 100 tends to be of higher molecular weight that the
hardwood lignosulfonate products disclosed herein. Furthermore, the
gangue depressant compositions of these patents are mixtures that include
additional ingredients as essential components, such as
chemically-modified carbohydrate polymers (e.g., causticized starch),
polyacrylates, quebracho, and dextrin. These patent do not disclose
specific lignosulfonates that function as efficiently as sodium cyanide
in gangue depressant compositions.

[0007]U.S. Pat. No. 5,575,334 also discloses the use of lignosulfonates
for recovering metal from ore. However, the '334 patent does not disclose
the use of specific lignosulfonates as described herein that function as
efficiently as sodium cyanide in gangue depressant compositions.

[0008]U.S. Pat. Nos. 4,731,113; and 4,645,535 disclose leaching lixiviant
compositions that include lignosulfonate. The compositions of these
patents are mixtures that include additional ingredients as essential
components, such as thiourea compounds and urea, and are used for
non-flotation applications. Furthermore, these patents do not disclose
specific lignosulfonates as described herein that function as efficiently
as sodium cyanide in gangue depressant compositions.

SUMMARY

[0009]Disclosed are compositions and methods for separating gangue
material from metallic sulfide ores. The compositions and methods
typically relate to froth flotation processes for recovering,
concentrating, or isolating metallic sulfide ores. The disclosed
compositions typically include and the methods utilize a lignosulfonate
and do not include a cyanide reagent (e.g., sodium cyanide). In some
embodiments, the compositions include and the methods utilize a
lignosulfonate comprising lignin obtained from a hardwood tree such as
Eucalyptus, Maple or Birch trees. The methods typically do not include
the use of a cyanide reagent (e.g., sodium cyanide), either as a gangue
depressant or otherwise. The lignosulfonates used in the disclosed
compositions and methods may have a relatively low sulfur or sulfonate
content in comparison to lignosulfonates disclosed in the prior art.

[0010]The disclosed compositions may be used in methods related to
recovering, concentrating, or isolating a metal sulfide from an ore. The
methods may include preparing an ore slurry or pulp composition which
includes: (a) ore, which optionally may be ground ore; (b) water; (c) a
lignosulfonate or a salt thereof (e.g., a lignosulfonate or a salt
thereof suitable as a gangue depressant); and (d) a processing reagent
(e.g., a processing agent that facilitates separation of the metallic
sulfide from gangue where the agent is selected from the group consisting
of a flotation reagent, a frothing reagent, a collector reagent, and an
extractor reagent.) In some embodiments, the processing reagent may
facilitate foaming of the ore slurry upon introduction of air into the
slurry. Typically, the slurry does not include cyanide or a salt thereof.
The lignosulfonate typically is a hardwood lignosulfonate having a weight
average molecular weight of about 3 kDa to about 12 kDa (preferably about
4 kDa to about 10 kDa, more preferably about 5.5 kDa to about 9 kDa). The
molecular weight of lignosulfonate may be determined by size exclusion
chromatography in combination with multi angle laser light scattering
detection.

[0011]In some embodiments, the disclosed compositions may include a
lignosulfonate having a relatively low sulfur or sulfonate content. For
example, the disclosed lignosulfonates may have a sulfur content of less
than about 10.0% (w/w) (preferably less than about 9.0% (w/w), or more
preferably less than about 8% (w/w)). In further examples, the disclosed
lignosulfonates may have a sulfonate content of less than about 7.5%
(w/w) (preferably less than about 7.0% (w/w), more preferably less than
about 6.5% (w/w), even more preferably less than about 6.0% (w/w)).

[0012]In some embodiments, the disclosed compositions may include a
lignosulfonate having a relatively low pH in aqueous solution. For
example, the disclosed lignosulfonates may have a pH of less than about
9.0 in aqueous solution. In other embodiments, the disclosed
lignosulfonates may have a pH of less than about 8.5, 8.0 or 7.5 in
aqueous solution.

[0013]The disclosed compositions may include lignosulfonate having a
relatively high purity. In some embodiments, the lignosulfonate may have
a relatively high purity as assessed by sugar content. In some
embodiments, the disclosed compositions may include lignosulfonate having
a sugar content of less than about 6.0% (w/w) (preferably less than about
5.0% (w/w), more preferably less than about 4.0% (w/w)).

[0014]In some embodiments, the disclosed compositions may include
lignosulfonate having a relatively high hydrophobicity or a relatively
low hydrophilicity in comparison to lignosulfonates in the prior art.
Hydrophobicity and hydrophilicity can be measured using methods known in
the art (e.g., hydrophobic interactive chromatography).

[0015]In some embodiments, the methods for recovering, concentrating, or
isolating a metal sulfide from an ore may include the following steps:
(a) adding a lignosulfonate or a salt thereof to the ore (e.g., a
lignosulfonate or a salt thereof suitable as a gangue depressant); (b)
adding at least one of a flotation reagent, a frothing reagent, a
collector reagent, and an extractor reagent to the ore; (c) preparing an
ore slurry, wherein the ore slurry has a pH that is basic; (d)
introducing air into the ore slurry to create a frothed fraction, wherein
the metal sulfide is at least partially suspended in the frothed
fraction; and (e) removing the frothed fraction from the ore slurry,
thereby recovering, concentrating, or isolating the metal sulfide;
wherein the method does not comprise adding cyanide or a salt thereof to
the ore or the ore slurry. Examples of metal sulfides recovered,
concentrated, or isolated in the disclosed methods may include copper
sulfides, zinc sulfides, lead sulfides, and mixtures thereof. Typically,
the lignosulfonates used in the methods is a hardwood derived
lignosulfonate having a weight average molecular weight of about 3 kDa to
about 12 kDa (preferably about 4 kDa to about 10 kDa, more preferably
about 5.5 kDa to about 9 kDa). Optionally, molecular weight may be
determined by size exclusion chromatography (SEC) and/or multi-angle
laser light scattering (MALLS). (See, e.g., Fredheim et al., J.
CHROMATOGR. A. 2002 Jan. 4; 942(1-2):191-9).

[0016]In other embodiments, the methods may include the following steps:
(a) preparing an ore slurry, (b) adding a lignosulfonate or a salt
thereof to the ore slurry (e.g., a lignosulfonate or a salt thereof
suitable as a gangue depressant); (c) adding at least one processing
reagent to the ore slurry, the processing agent selected from the group
consisting of a flotation reagent, a frothing reagent, a collector
reagent, an extractor reagent and combinations thereof; (d) introducing
air into the ore slurry to create a frothed fraction, where the metal
sulfide is at least partially suspended in the frothed fraction; and (e)
removing the frothed fraction from the ore slurry, thereby recovering,
concentrating, or isolating the metal sulfide.

[0017]The gangue depressants disclosed herein may include lignosulfonate
or a salt thereof. In some embodiments, the gangue depressant may consist
of a lignosulfonate or a salt thereof. The gangue depressant may include
a lignosulfonate comprising lignin obtained from a hardwood lignin tree.
In some embodiments, suitable lignosulfonates a hardwood lignosulfonate
(e.g., lignosulfonate derived from Eucalyptus, Maple or Birch lignin)
having a weight average molecular weight of about 3 kDa to about 12 kDa
(preferably about 4 kDa to about 10 kDa, more preferably about 5.5 kDa to
about 9 kDa). Lignosulfonate salts may include but are not limited to
sodium salts, potassium salts, and calcium salts.

[0018]In some embodiments, the disclosed methods relate to the use of
lignosulfonates to replace hazardous or toxic depressants or to replace
more complex mixtures of depressants for the separation of gangue
material from valuable sulfide ores. Typically, the compositions do not
include and the methods do not utilize a cyanide reagent such as sodium
cyanide. In some embodiments, the methods do not include adding cyanide
or a salt thereof (e.g., sodium cyanide) to the ore or the ore slurry
(e.g., as a gangue depressant).

[0019]The lignosulfonates or salts thereof used in the disclosed
compositions and methods may function as a gangue depressant (e.g., the
lignosulfonates or salts thereof may be present at a concentration
effective for depressing gangue in a flotation method for isolating a
metallic sulfide). In some embodiments, the lignosulfonates function
effectively as gangue depressants such that the composition does not
include and the methods do not utilize additional reagents as gangue
depressants. Typically, the compositions do not include and the methods
do not utilize a cyanide (e.g., sodium cyanide), either as a gangue
depressant or otherwise. In some embodiments, the compositions do not
include and the methods do not utilize a chemically-modified carbohydrate
such as a starch or dextrin which has been treated with an alkaline
solution (e.g., a solution having a pH of about 12 to about 14), either
as a gangue depressant or otherwise. In further embodiments, the
compositions do not include and the methods do not utilize a
polyacrylate, quebracho, dextrin, or guar gum, either as a gangue
depressant or otherwise.

[0020]Lignosulfonates used in the compositions and methods may be added at
an effective concentration for achieving a desired recovery rate and
grade for a selected metal ore in a frothed fraction of an ore slurry.
Lignosulfonates used in the compositions and methods may be added at an
effective concentration for achieving gangue depression. For example,
effective concentrations of lignosulfonates used in the compositions and
methods may include but are not limited to at least about 50, 100, 175,
250, 325, 500, 1000, 1500, or 2000 grams per metric ton ore (g/mt).
Ranges of concentrations for the lignosulfonates present in an ore or ore
slurry are contemplated (e.g., ranges having as end-point concentrations
about 50, 100, 175, 250, 325, 500, 1000, 1500, or 2000 g/mt, such as the
ranges 250-500, 500-1000, and 1000-1500 g/mt).

[0021]The prepared ore slurry may include reagents to facilitate
concentrating, isolating, or recovering metallic sulfides. For example,
the prepared ore slurry may include reagents for adjusting or buffering
the pH of the slurry. In some embodiments, the prepared ore slurry has a
pH that is basic. For example, the methods may include adding a reagent
to the ore or the ore slurry for increasing the pH of the ore slurry. In
some embodiments, the prepared ore slurry has a pH that is greater than
about 8 (or in further embodiments greater than about 10). The prepared
ore slurry may have pH within a desirable range (e.g., about 9.5 to about
11.5). Additional reagents which may be added to the ore or the ore
slurry include, but are not limited to, carbonates (e.g., sodium
carbonate or soda ash), and hydroxides (e.g., calcium hydroxide or lime).

[0022]Typically, the disclosed compositions include and the methods
utilize a processing reagent, which may be added to the ore or the ore
slurry. The processing agent may be selected from the group consisting of
a flotation reagent, a frothing reagent, a collector reagent, an
extractor reagent, and combinations thereof. In some embodiments, the
processing agent may include a surfactant. The processing reagent may
include an aliphatic alcohol having 3-12 carbons which may be
straight-chain, branched, or cyclic. For example, the additional reagent
may include methylisobutylcarbinol (MIBC). The processing reagent may
include a xanthate (e.g., sodium isopropyl xanthate). In further
embodiments, the processing reagents may include a reagent selected from
the group consisting of a phosphate (e.g., calcium phosphate), a sulfate
(e.g., copper sulfate), a thionocarbamate, a thiophosphate, a thiourea,
and combinations thereof.

[0023]In some embodiments, the methods relate to recovering copper (e.g.,
as copper sulfide) from an ore. The methods may be effective for
recovering at least about 50, 55, 60, 65, or 70% (w/w) total copper from
an ore where the copper grade is at least about 10, 15, or 20% (w/w) in a
frothed fraction of an ore slurry.

[0024]In some embodiments, the methods relate to recovering zinc (e.g., as
zinc sulfide) from an ore. The methods may be effective for recovering at
least about 50, 55, 60, 65, or 70% (w/w) total zinc from an ore where the
zinc grade is at least about 10, 15, or 20% (w/w) in a frothed fraction
of an ore slurry.

[0025]In some embodiments, the methods relate to recovering lead (e.g., as
lead sulfide) from an ore. The methods may be effective for recovering at
least about 50, 55, 60, 65, or 70% (w/w) total lead from an ore where the
lead grade is at least about 10, 15, or 20% (w/w) in a frothed fraction
of an ore slurry.

[0026]Typically, the methods are effective for recovering, concentrating,
or isolating a selected metal sulfide (e.g., copper sulfide, zinc
sulfide, or lead sulfide) in a frothed fraction of an ore pulp or slurry
and likewise are effective for removing or reducing iron compounds such
as pyrrhotite, pyrite, and marcasite in a frothed fraction from an ore
pulp or slurry. In some embodiments, the methods recover no more than
about 20% (w/w) total iron from an ore slurry (based on iron present in a
frothed fraction of the ore slurry). Preferably, the methods recover no
more than about 18, 16, 14, 12, or 10% (w/w) total iron from an ore
slurry. The methods may produce a frothed fraction of the ore slurry that
has an enriched concentration of a selected metal sulfide (e.g., copper
sulfide, zinc sulfide, or lead sulfide) versus iron compounds (e.g.,
pyrrhotite, pyrite, or marcasite), relative to the concentrations of the
selected metal sulfide and iron compound in the total ore slurry.

[0027]Also disclosed are lignosulfonates. The disclosed lignosulfonates
may include purified hardwood lignosulfonate (e.g., lignosulfonate
derived from Eucalyptus, Maple or Birch lignin) having a weight average
molecular weight of about 3 kDa to about 12 kDa (preferably about 4 kDa
to about 10 kDa, more preferably about 5.5 kDa to about 9 kDa).

[0034]The present invention is described herein using several definitions,
as set forth below and throughout the application.

[0035]As used herein, "about", "approximately," "substantially," and
"significantly" will be understood by persons of ordinary skill in the
art and will vary to some extent on the context in which they are used.
If there are uses of the term which are not clear to persons of ordinary
skill in the art given the context in which it is used, "about" and
"approximately" will mean plus or minus ≦10% of the particular
term and "substantially" and "significantly" will mean plus or minus
>10% of the particular term.

[0036]As used herein, the term "lignin" has its normal connotation, and
refers to an amorphous polymer that occurs in woody material of higher
plants such as trees. Lignin is composed of phenylpropanol groups
(typically p-phenylpropanol groups) that are linked by various
carbon-carbon linkages and ether linkages. Optionally, the phenyl moiety
of the phenylpropanol group further is substituted by one or more methoxy
groups adjacent to the phenyl moiety's hydroxyl group. The phenylpropanol
groups of softwood lignin typically include fewer methoxy substitutions
on the phenyl moiety (typically having one or no methoxy substitutions)
than phenylpropanol groups of hardwood lignin (typically having two
methoxy substitutions). Hardwood and softwood lignosulfonates can most
easily be distinguished by UV (ultraviolet) analysis, as each type of
lignosulfonate displays a characteristic absorption in the UV spectrum.
Hardwood lignosulfonates typically display a UV maximum (λmax) from
276 to 277 nm in their UV spectrum, while softwood lignosulfonates
typically display this maximum from 280 to 281 nm. In some embodiments,
the hardwood lignosulfonates utilized in the presently disclosed
compositions and methods may display a UV maximum from 276-277 nm.

[0037]Lignin typically is recovered from the organosolve process, or from
alkaline black pulping liquors such as are produced in the Kraft, soda,
and other well known alkaline pulping operations. The term "sulfonated
lignin," as used in this specification, refers to the product which is
obtained by the introduction of sulfonic acid groups into the lignin
molecule, as may be accomplished by the reaction of lignin with sulfite
or bisulfite compounds. For example, the waste liquors from such
organosolve or alkaline pulping contain large quantities of lignin and
lignin decomposition products, which can be sulfonated or sulfomethylated
by known processes, such as high temperature sulfonation, oxidative
sulfonation at ambient temperature, or sulfomethylation by reaction of
lignin, sodium sulfite and formaldehyde. As used herein, the term
"sulfite lignin" refers to the reaction product of lignin, which is
inherently obtained during sulfite pulping of wood, straw, corn stalks,
bagasse and the like, and is a principle constituent of the spent sulfite
liquor which is derived from that process. The phrases "lignosulfonate"
and "lignin sulfonate" may be used interchangeably herein and include the
sulfonated lignin and sulfite lignin reaction products described above,
and also spent sulfite liquors that may be further reacted, purified,
fractionated, or the like, as may be required to produce the
lignosulfonate material of interest. The lignosulfonates may be utilized
in the "as is" or whole liquor condition. They may also be utilized as a
purified lignosulfonate material from, or in which the sugars and other
saccharide constituents have been removed and/or destroyed, or
additionally inorganic constituents have been partially or fully
eliminated. Lignosulfonates may be utilized in their salt form. For
example, calcium lignosulfonates, sodium lignosulfonates, ammonium
lignosulfonates, potassium lignosulfonates, magnesium lignosulfonates and
mixtures or blends thereof. Lignosulfonates are available from numerous
sources in either solution or dried power forms.

[0038]The disclosed compositions may include a lignosulfonate having a
relatively low sulfur or sulfonate content. A lignosulfonate having "a
relatively low sulfur content" may have a sulfur content of less than
about 10.0% (w/w) (preferably less than about 9.0% (w/w), or more
preferably less than about 8% (w/w)). A lignosulfonate having "a
relatively low sulfonate content" may have a sulfonate content of less
than about 7.5% (w/w) (preferably less than about 7.0% (w/w), or more
preferably less than about 6.5% (w/w)).

[0039]The disclosed compositions may include a lignosulfonate having a
relatively low pH in aqueous solution. A lignosulfonate having a
relatively low pH in solution may have a pH of less than about 9.0 in
aqueous solution (and preferably has a pH of less than about 8.5, 8.0 or
7.5 in aqueous solution).

[0040]The disclosed compositions and methods may utilize or include a
purified sulfonated lignin. As disclosed herein, a "purified sulfonated
lignin" may include a sulfonated lignin in which contaminants such as
sugars and phenolic monomers and oligomers (e.g., polymers having fewer
than about 10 monomers) have been removed such that at least about 90% of
the dry matter is composed of sulfonated lignin salt (preferably at least
about 95% of the dry matter is composed of sulfonated lignin salt).
Optionally, high purity sulfonated lignin may be obtained by performing
methods that include fermenting and/or ultrafiltering. Fermentation may
be performed to provide lignosulfonate having a sugar content of less
than about 6.0% (w/w) (preferably less than about 5.0% (w/w), and more
preferably less than about 4.0% (w/w)). Purity may be assessed by
determining methoxyl content of the lignosulfonate material. In some
embodiments, the methoxyl content of lignosulfonate salt may be measured
and corrected for the weight of the associated sulfonic groups and salt
cation to calculate the purity of the sulfonated lignin salt using the
typical methoxyl content of lignin in the calculation (e.g., about 14.6%
methoxyl content for softwood lignin and about 21.4% methoxyl content for
hardwood lignin).

[0041]The disclosed compositions and methods may utilize or include low
molecular weight sulfonated lignin. Optionally, molecular weight may be
determined by size exclusion chromatography (SEC) and/or multi-angle
laser light scattering (MALLS). (See, e.g., Fredheim et al., J.
CHROMATOGR. A. 2002 Jan. 4; 942(1-2):191-9 "Molecular weight
determination of lignosulfonates by size exclusion chromatography and
multi-angle laser light scattering"). As disclosed herein, a "high
molecular weight sulfonated lignin" typically has a molecular weight that
is greater than about 20 kDa (preferably greater than about 30 kDa, more
preferably greater than about 40 kDa, and even more preferably greater
than about 50 kDa), A "low molecular weight sulfonated lignin" typically
has a molecular weight that is no more than about 20 kDa (preferably no
more than 12 kDa, or more preferably no more than about 10 kDa).

[0042]The lignosulfonates used in the disclosed methods may be hardwood
lignosulfonates. For example, the lignosulfonates used in the disclosed
methods may comprise lignin isolated from the hardwood Eucalyptus, Maple
or Birch trees. The hardwood lignosulfonates used in the disclosed
methods typically have a weight average molecular weight of about 3 kDa
to about 12 kDa (preferably about 4 kDa to about 10 kDa, more preferably
about 5.5 kDa to about 9 kDa);

[0043]The lignosulfonates disclosed herein may be used in froth flotation
methods as a gangue depressant. As used herein, a gangue depressant
reduces the amount of floatable gangue (e.g., iron-containing compounds
such as pyrrhotite, pyrite, or marcasite) in a froth flotation method for
recovering metallic sulfides (e.g., copper, zinc, or lead sulfides). In
froth flotation methods, a gangue depressant typically is effective at
reducing the amount of a gangue material in the froth of an ore pulp or
slurry, relative to an ore pulp or slurry that does not include a gangue
depressant. Gangue depressant activity may be assessed by calculating a
ratio x %/y %, where "x %" is the percentage recovery in the froth of a
selected metallic sulfide relative to the total amount of the selected
metallic sulfide in the ore slurry; and "y %" is the percentage recovery
in the froth of gangue material relative to the total amount of the
gangue material in the ore slurry. The lignosulfonates used in the
disclosed methods may exhibit superior gangue depressant activity in
comparison to other gangue depressants and other lignosulfonates (e.g.,
in comparison to technical grade softwood lignosulfonates).

[0044]The lignosulfonates disclosed herein may be added to an ore or an
ore slurry at an effective amount of lignosulfonates per metric ton ore
(e.g., g/mt effective for gangue depression). For example, the
lignosulfonates may be added at an amount including, but not limited to
about 50, 100, 175, 225, 350, 500, 1000, 1500, or 2000 g/mt ore (or
ranges of these concentrations as contemplated herein). The
lignosulfonates may be added to an ore or an ore slurry at an effective
amount per metric ton ore in order to achieve a desired result (e.g.,
gangue depression). In some embodiments, the lignosulfonates may be added
at an effective amount in order to achieve a reduction in the percentage
of gangue recovered in a froth fraction versus total gangue in an ore
slurry. For example, the lignosulfonates may be added at an amount of no
more than about 2000 g/mt, 1500, g/mt, 1000 g/mt, or 500 g/mt (or
preferably no more than about 325 g/mt, 250 g/mt, 175 g/mt, 100 g/mt, or
50 g/mt) (or ranges of these concentrations as contemplated herein) to
achieve a reduction in the percentage gangue recovered in a froth
fraction versus total gangue in an ore slurry of at least about 30% (or
preferably at least about 40% and more preferably at least about 50%).

[0046]As used herein, the term "alkyl" denotes a straight-chain or
branched alkyl radical having 1-22 carbons (preferably having 1-18, 1-12,
or 1-6 carbons), in all its isomeric forms. As used herein, the term
"alkenyl" denotes a straight-chain or branched alkenyl radical having
2-22 carbons (preferably having 2-18, 2-12, or 2-6 carbons), in all its
isomeric forms.

ILLUSTRATIVE EMBODIMENTS

[0047]The following embodiments are illustrative and are not intended to
limit the disclosed subject matter.

Embodiment 1

[0048]An ore slurry comprising: (a) sulfide ore; (b) water; (c) a
lignosulfonate or a salt thereof (e.g., a lignosulfonate or a salt
thereof suitable as a gangue depressant), wherein the lignosulfonate is
isolated from a hardwood lignin tree and has a weight average molecular
weight of about 3 kDa to about 12 kDa (preferably about 4 kDa to about 10
kDa, more preferably about 5.5 kDa to about 9 kDa); and (d) a processing
reagent selected from the group consisting of a flotation reagent, a
frothing reagent, a collector reagent, and an extractor reagent; wherein
the slurry does not comprise cyanide or a salt thereof.

[0052]The ore slurry of any of embodiments 1-4, wherein the ore comprises
lead sulfide.

Embodiment 6

[0053]The ore slurry of any of embodiments 1-5, wherein the ore comprises
an iron compound selected from the group consisting of pyrrhotite,
pyrite, and marcasite.

Embodiment 7

[0054]The ore slurry of any of embodiments 1-6, wherein the slurry has a
pH that is greater than about 8.

Embodiment 8

[0055]The ore slurry of any of embodiments 1-7, wherein the slurry has a
pH that is greater than about 10.

Embodiment 9

[0056]The ore slurry of any of embodiments 1-8, wherein the slurry has a
pH that is between about 9.5 and about 11.5.

Embodiment 10

[0057]The ore slurry of any of embodiments 1-9, wherein the slurry
comprises lignosulfonate or the salt thereof as a gangue depressant and
comprises no other gangue depressant.

Embodiment 11

[0058]The ore slurry of any of embodiments 1-10, wherein the salt of the
lignosulfonate is selected from the group consisting of sodium
lignosulfonate, potassium lignosulfonate, calcium lignosulfonate, or
mixtures thereof.

Embodiment 12

[0059]The ore slurry of any of embodiments 1-11, wherein the flotation
reagent, the frothing reagent, the collector reagent, or the extractor
reagent comprises an aliphatic alcohol having 3-12 carbons which may be
straight-chain, branched, or cyclic.

[0061]The ore slurry of any of embodiments 1-13, wherein the flotation
reagent, the frothing reagent, the collector reagent, or the extractor
reagent comprises a xanthate.

Embodiment 15

[0062]The ore slurry of any of embodiments 1-14, wherein the flotation
reagent, the frothing reagent, the collector reagent, or the extractor
reagent comprises a reagent selected from the group consisting of a
thionocarbamate, a thiophosphate, and a thiourea.

Embodiment 16

[0063]The ore slurry of any of embodiments 1-15, further comprising sodium
carbonate.

Embodiment 17

[0064]The ore slurry of any of embodiments 1-16, further comprising
calcium hydroxide.

Embodiment 18

[0065]The ore slurry of any of embodiments 1-17, wherein the slurry does
not comprise starch or dextrin which has been treated with an alkaline
solution.

Embodiment 19

[0066]The ore slurry of any of embodiments 1-18, wherein the slurry does
not comprise a polyacrylate.

Embodiment 20

[0067]The ore slurry of any of embodiments 1-19, wherein the slurry does
not comprise quebracho, dextrin, or guar gum.

Embodiment 21

[0068]The ore slurry of any of embodiments 1-20, wherein the slurry
comprises an effective amount of the lignosulfonate or a salt thereof for
depressing gangue in a flotation method for isolating metal sulfide from
the ore.

Embodiment 22

[0069]A method of recovering a metal sulfide from an ore, the method
comprising: (a) adding a lignosulfonate or a salt thereof to the ore
(e.g., a lignosulfonate or a salt thereof suitable as a gangue
depressant), wherein the lignosulfonate comprises a hardwood
lignosulfonate (e.g., a purified hardwood lignosulfonate) having a weight
average molecular weight of about 3 kDa to about 12 kDa (preferably about
4 kDa to about 10 kDa, more preferably about 5.5 kDa to about 9 kDa); (b)
adding at least one of a flotation reagent, a frothing reagent, a
collector reagent, and an extractor reagent to the ore; (c) preparing an
ore slurry, wherein the ore slurry has a pH that is basic; (d)
introducing air into the ore slurry to create a frothed fraction, wherein
the metal sulfide is at least partially suspended in the frothed
fraction; and (e) removing the frothed fraction from the ore slurry,
thereby recovering the metal sulfide; wherein the method does not
comprise adding cyanide or a salt thereof to the ore or the ore slurry.

[0073]The method of any of embodiments 22-25, wherein the metal sulfide
comprises lead sulfide.

Embodiment 27

[0074]The method of any of embodiments 22-26, wherein the ore slurry has a
pH that is greater than about 8.

Embodiment 28

[0075]The method of any of embodiments 22-27, wherein the ore slurry has a
pH that is greater than about 10.

Embodiment 29

[0076]The method of any of embodiments 22-28, wherein the ore slurry has a
pH that is between about 9.5 and about 11.5.

Embodiment 30

[0077]The method of any of embodiments 22-29, wherein the ore slurry
comprises lignosulfonate or the salt thereof as a gangue depressant and
comprises no other gangue depressant.

Embodiment 31

[0078]The method of any of embodiments 22-30, wherein the salt of the
lignosulfonate is selected from the group consisting of sodium
lignosulfonate, potassium lignosulfonate, calcium lignosulfonate, or
mixtures thereof.

Embodiment 32

[0079]The method of any of embodiments 22-31, wherein the flotation
reagent, the frothing reagent, the collector reagent, or the extractor
reagent comprises an aliphatic alcohol having 3-12 carbons which may be
straight-chain, branched, or cyclic.

[0081]The method of any of embodiments 22-33, wherein the flotation
reagent, the frothing reagent, the collector reagent, or the extractor
reagent comprises a xanthate.

Embodiment 35

[0082]The method of any of embodiments 22-34, wherein the flotation
reagent, the frothing reagent, the collector reagent, or the extractor
reagent comprises a reagent selected from the group consisting of a
thionocarbamate, a thiophosphate, and a thiourea.

Embodiment 36

[0083]The method of any of embodiments 22-35, further comprising adding
sodium carbonate to the ore or the ore slurry.

Embodiment 37

[0084]The method of any of embodiments 22-36, further comprising adding
calcium hydroxide to the ore or the ore slurry.

Embodiment 38

[0085]The method of any of embodiments 22-37, wherein the method does not
comprise adding to the ore or the ore slurry a starch or dextrin which
has been treated with an alkaline solution.

Embodiment 39

[0086]The method of any of embodiments 22-38, wherein the method does not
comprise adding to the ore or the ore slurry a polyacrylate.

Embodiment 40

[0087]The method of any of embodiments 22-39, wherein the method does not
comprise adding to the ore or the ore slurry quebracho, dextrin, or guar
gum.

Embodiment 41

[0088]The method of any of embodiments 22-40, wherein the slurry comprises
an effective amount of the lignosulfonate or a salt thereof for
depressing gangue in a flotation method for isolating metal sulfide from
the ore.

Embodiment 42

[0089]A method of recovering a metal sulfide from an ore, the method
comprising: (a) preparing an ore slurry, wherein the ore slurry has a pH
that is basic; (b) adding a lignosulfonate or a salt thereof to the ore
slurry (e.g., a lignosulfonate or a salt thereof suitable as a gangue
depressant), wherein the lignosulfonate comprises a hardwood
lignosulfonate (e.g., a purified hardwood lignosulfonate derived from
Eucalyptus, Maple or Birch hardwood lignosulfonate) having a weight
average molecular weight of about 3 kDa to about 12 kDa (preferably about
4 kDa to about 10 kDa, more preferably about 5.5 kDa to about 9 kDa); (c)
adding at least one of a flotation reagent, a frothing reagent, a
collector reagent, and an extractor reagent to the ore slurry; (d)
introducing air into the ore slurry to create a frothed fraction, wherein
the metal sulfide is at least partially suspended in the frothed
fraction; and (e) removing the frothed fraction from the ore slurry,
thereby recovering the metal sulfide; wherein the method does not
comprise adding cyanide or a salt thereof to the ore or the ore slurry.

[0093]The method of any of embodiments 42-45, wherein the metal sulfide
comprises lead sulfide.

Embodiment 47

[0094]The method of any of embodiments 42-46, wherein the ore slurry has a
pH that is greater than about 8.

Embodiment 48

[0095]The method of any of embodiments 42-47, wherein the ore slurry has a
pH that is greater than about 10.

Embodiment 49

[0096]The method of any of embodiments 42-48, wherein the ore slurry has a
pH that is between about 9.5 and about 11.5.

Embodiment 50

[0097]The method of any of embodiments 42-49, wherein the gangue
depressant consists of the lignosulfonate or the salt thereof.

Embodiment 51

[0098]The method of any of embodiments 42-50, wherein the salt of the
lignosulfonate is selected from the group consisting of sodium
lignosulfonate, potassium lignosulfonate, calcium lignosulfonate, or
mixtures thereof.

Embodiment 52

[0099]The method of any of embodiments 42-51, wherein the flotation
reagent, the frothing reagent, the collector reagent, or the extractor
reagent comprises an aliphatic alcohol having 3-12 carbons which may be
straight-chain, branched, or cyclic.

[0101]The method of any of embodiments 42-53, wherein the flotation
reagent, the frothing reagent, the collector reagent, or the extractor
reagent comprises a xanthate.

Embodiment 55

[0102]The method of any of embodiments 42-54, wherein the flotation
reagent, the frothing reagent, the collector reagent, or the extractor
reagent comprises a reagent selected from the group consisting of a
thionocarbamate, a thiophosphate, and a thiourea.

Embodiment 56

[0103]The method of any of embodiments 42-55, further comprising adding
sodium carbonate to the ore or the ore slurry.

Embodiment 57

[0104]The method of any of embodiments 42-56, further comprising adding
calcium hydroxide to the ore or the ore slurry.

Embodiment 58

[0105]The method of any of embodiments 42-57, wherein the method does not
comprise adding to the ore or the ore slurry a starch or dextrin which
has been treated with an alkaline solution.

Embodiment 59

[0106]The method of any of embodiments 42-58, wherein the method does not
comprise adding to the ore or the ore slurry a polyacrylate.

Embodiment 60

[0107]The method of any of embodiments 42-59, wherein the method does not
comprise adding to the ore or the ore slurry quebracho, dextrin, or guar
gum.

Embodiment 61

[0108]The method of any of embodiments 42-60, wherein the slurry comprises
an effective amount of the lignosulfonate or a salt thereof for
depressing gangue in a flotation method for isolating metal sulfide from
the ore.

EXAMPLES

[0109]The following examples are illustrative and are not intended to
limit the disclosed subject matter.

Example 1

Preparation of Lignosulfonate Products

[0110]Two lignosulfonate products were prepared, D-748 and D-912. The
D-748 product was prepared by fermenting softwood lignosulfonate and
subsequently subjecting the fermented softwood lignosulfonate to
ultrafiltration. The D-912 product was derived from hardwood
lignosulfonate and was processed in order to remove a substantial portion
of the oxidizable sugars that are commonly present in technical grade
lignosulfonate. Table 1 provides an analytical summary of the D-748 and
D-912 products and for comparison, Kelig 100, which is observed to have a
higher sulfur content and sulfonate content.

[0111]A sulfide ore from a mine in Peru was tested and contained
approximately 4.2% copper and 4.8% zinc. This ore was subjected to
flotation under the following standard conditions.

[0112]All samples were riffle split into 1000 gram charges from an ore
sample passing 6-mesh. For each flotation sample, the ore was ground for
such a time that 80% of the ore passed 150 mesh screen. Slake lime was
used as a pH modifier and added to the grinding phase, as were the
lignosulfonate products D-912 and D-748 as gangue depressant. (See Table
2 for description of samples.)

[0113]After grinding, a collector (Aero promoter AP3894) and MIBC
(methylisobutylcarbinol) were added, and the pulp was conditioned for a
time of 3 minutes. This was followed by recovery of the concentrate
(frothed fraction) via froth flotation for 8 minutes using a Denver
laboratory flotation cell. The pulp density was determined as 25%.

[0114]The collected froth was analyzed and yielded the results shown in
Tables 3 and 4. Samples 2 and 3 included sodium cyanide at two
concentrations. Samples 4-7 and Samples 8 and 9 included lignin products
D-912 and D-748, respectively, at several concentrations.

[0115]The % recovery vs. % grade were plotted for each metal and compared
to the samples that included sodium cyanide (250 and 325 g/MT) (See FIGS.
1 and 2.) The results indicated that both additives D-912 and D-748
display gangue depressant activity. In the case of copper the depression
activity was similar to sodium cyanide, and in the case of zinc the
depression activity was superior to sodium cyanide. Use of the D-912
additive resulted in a decrease of iron recovery (%) ranging from 48-69%
(at least about 45%) in comparison to Sample 1, where no additive was
used. (See Table 5.)

Example 3

Zinc/Lead Sulfide Ore

[0116]A sulfide ore from a mine in Peru was tested and contained
approximately 0.7% lead, 13% zinc and 15% iron. The ore was subjected to
flotation under the following conditions.

[0117]The testing was performed using a Denver laboratory flotation cell
per the conditions described in Table 6.

[0118]The separation consisted of three stages with the first flotation
step designed to remove unwanted carbon, the second step designed to
recover lead, and the final step designed to recover zinc. All samples
were riffle split into 2000 g charges from an ore sample passing a 10
mesh screen. For each flotation sample, the ore was ground for such a
time that 55% of the ore passed a 200 mesh screen. Slake lime was used
throughout the flotation experiments to keep the pH at 11±0.2.

[0120]The data indicates that the D-912 and D-748 products have gangue
depressant activity and provide a concentrated ore fraction having a
higher lead or zinc % recovery relative to iron % recovery than the
sample having no gangue depressant. In addition, the D-912 and D-748
products displayed superior gangue depressant activities in comparison to
sodium cyanide for zinc.

Example 4

Effect of Soda Ash in Combination with Lignosulfonate

[0121]The same flotation procedure used in Example 2 was used in this
example except that soda ash rather than slake lime was used as a pH
modifier to bring the pH of the system to about 10. Sodium carbonate
(soda ash) was used as the pH modifier to measure the effect of rendering
most divalent ions (e.g., calcium cations) in the sample insoluble during
the flotation process. Soda ash was added to the grinding phase, as were
the gangue depressants. After grinding, a collector (Aero promoter
AP3894) and MIBC (methylisobutylcarbinol) were added, and the pulp was
conditioned for a time of 3 minutes. This was followed by recovering the
concentrate (frothed fraction) via froth flotation for 8 minutes using a
Denver laboratory flotation cell. The pulp density was determined to be
25%.

[0122]The collected froth was analyzed and yielded the results shown in
Table 8 as well as FIGS. 3 and 4, which indicate that soda ash improves
the grade % for recovered copper and zinc, respectively.

[0123]A copper containing sulfide ore from Arizona was subjected to
selective flotation. This ore contained approximately 0.4% copper and
0.9% iron. The following flotation procedure was used.

[0124]A large sample of crude ore was crushed such that it passing a 10
mesh screen. All flotation samples were riffle split from this large
sample into 1000 gram charges. For each test the 1000 gram ore charge was
place in a laboratory rod mill, combined with 666 g water and 1.1 g
Ca(OH)2. Pyrite depressants (0.1 lbs./MT) were also added to mill
prior milling. The ore, water, lime and depressant were milled until 40%
of the ore material passed 65 mesh screen. The slurry was immediately
placed in a Denver Laboratory Flotation Cell and subjected to froth
flotation. A collector was added (0.01 gram Cytec 10059) and the sample
conditioned at 1300 rpm for 1 minute. Following this conditioning step, a
frother was immediately added (0.015 g Cytec X133) and the sample was
again conditioned for 1 minute. After these conditioning steps, two
separate flotation concentrates were collected. A rougher concentrate was
collected for 1 minute. This was immediately followed by collection of a
scavenger concentrate over 5 minutes. The rougher, scavenger and tails
were collected and dried. A portion of each fraction was subjected to
acid digestion in a microwave digester, followed by analysis by ICP for
copper and iron content. The analytical results are displayed in Table 9.

[0126]The data illustrate that D-912 rejected more iron than the control
which lacked depressant, and that D-912 rejected more iron than sodium
cyanide. Furthermore, using D-912 as a depressant, a higher grade and
recovery of Copper from this ore was obtained. The data also show that
D-912 is superior to Kelig 100 or the softwood lignosulfonate D-748 in
terms of iron rejection and copper concentration.